Liquid crystal display and fabricating method thereof

ABSTRACT

A liquid crystal display (LCD) and fabricating method thereof. The LCD includes a first substrate, provided with a plurality of parallel gate lines and a plurality of parallel signal lines, wherein the gate lines and signal lines are perpendicular, and a pixel area is defined by two adjacent gate lines and two adjacent signal lines. A source electrode, electrically connected to one of the adjacent signal lines, and a drain electrode are formed on the pixel area. A first pixel electrode is formed, electrically connected to the drain electrode, on the pixel area. A second substrate is provided a predetermined distance above the first substrate, having a plurality of color-filtering areas, directly above the respective pixel area. A second pixel electrode layer is formed on the second substrate, wherein the part thereof directly above the signal lines is relatively thin.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display, and moreparticularly to a liquid crystal display with reduced crosstalk.

2. Description of the Related Art

Liquid crystal display (LCD) is a commonly used flat panel display.Owing to dielectric anisotropy and conductive anisotropy of liquidcrystal molecules, molecular orientation of liquid crystals can beshifted under an external electronic field, such that various opticaleffects are produced.

A LCD panel is generally made up of two substrates, with a certain gappreserved therebetween, and a liquid crystal layer filled within thegap. Respective electrodes are formed on the two substrates,respectively, to control the orientation and oriental shift of liquidcrystal molecules.

A TFT (thin film transistor) LCD panel is generally made up of a TFTarray substrate and a color filter substrate. The detailed structuresare described as follows.

FIG. 1 is a top view showing a conventional TFT array substrate. FIG. 2is a cross-section taken at the line I—I in FIG. 1. In the manufactureof TFT array substrate, an insulating substrate 101, made of, forexample, glass or quartz, is provided. A gate electrode 108 and aninsulating layer 107 (not shown in FIG. 1) are then formed sequentiallyon the insulating substrate 101. Then, a channel layer 106 is formed onthe insulating layer 107, and a source electrode 102 and drain electrode103 are formed on the channel layer 106, respectively. Afterward, signallines 104 and pixel electrodes 105 are formed on the insulating layer107, electrically coupling to the source electrode 102 and drainelectrode 103, respectively.

FIG. 3 is a cross-section taken at the line II—II in FIG. 1, showing thecross-section of the signal line 104.

FIG. 4 illustrates the structure of the color filter substrate. Thecolor filter substrate includes a glass substrate 201, a black matrix(BM) 202 for anti-reflection, color-filtering units of red 203, green204, and blue 205, and a sputtered pixel electrode layer 206 as acorresponding electrode to the pixel electrode 105 of TFT arraysubstrate. The shapes, sizes, colors, and arrangements of thecolor-filtering units are adjustable according to requirements. Thepixel electrode layer 206 is a transparent conductive layer of, forexample, indium tin oxide layer.

After the separate manufacture of the TFT array substrate and colorfilter substrate, the two substrates are then aligned and joined with agap therebetween, and liquid crystal is filled into the gap to form theliquid crystal layer 3, thereby completeing the TFT panel fabrication.

FIG. 5 is a cross-section of the TFT panel taken at the line II—II inFIG. 1.

Due to the full coverage of pixel electrode layer 206 on the uppersubstrate 201, the pixel electrode 206 is formed against the signallines 104 at the same time. The pixel electrode layer 206 and signallines 104 are made of metal. Two layers of metal with dielectricmaterial, i.e. the liquid crystal layer 3, inserted therebetween, resultin capacitor effect, which weakens the signals, produces crosstalk,deteriorating display quality and affecting yield. Moreover, crosstalkbecomes more serious in larger display panels.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to reduce crosstalk,thereby ameliorating display quality problems.

Therefore, in the invention, the pixel electrode layer on the colorfilter substrate is thinned or removed above the signal lines on the TFTarray substrate to reduce coupling capacitance between the pixelelectrode on the color filter substrate and the signal lines on the TFTarray substrate, reducing crosstalk, improving display quality, andincreasing performance and yield.

The invention provides a liquid crystal display, which comprises a firstsubstrate, provided with a plurality of parallel gate lines and aplurality of parallel signal lines formed thereon, wherein the gatelines and signal lines are perpendicular, and a pixel area is defined bytwo adjacent gate lines and two adjacent signal lines. A sourceelectrode and a drain electrode are formed on the pixel area, whereinthe source electrode is electrically connected to one of the twoadjacent signal lines, and a first pixel electrode is formed on thepixel area, electrically connected to the drain electrode. A secondsubstrate is provided a predetermined distance above the firstsubstrate, having a plurality of color-filtering areas, each formeddirectly above the respective pixel area on the first substrate. Asecond pixel electrode layer is formed on the second substrate, whereinthe part of the second pixel electrode layer directly above the signallines is relatively thin.

The invention further provides a liquid crystal display, which comprisesa first substrate, provided with a plurality of parallel gate lines anda plurality of parallel signal lines formed thereon, wherein the gatelines and signal lines are perpendicular, and a pixel area is defined bytwo adjacent gate lines and two adjacent signal lines. A sourceelectrode and a drain electrode are formed on the pixel area, whereinthe source electrode is electrically connected to one of the twoadjacent signal lines, and a first pixel electrode is formed on thepixel area, electrically connected to the drain electrode. A secondsubstrate is provided a predetermined distance above the firstsubstrate, having a plurality of color-filtering areas, each formeddirectly above the respective pixel area on the first substrate. Asecond pixel electrode layer is formed on the second substrate, whereinthe part of the second pixel electrode layer directly above the signallines is hollow.

A method of fabricating a liquid crystal display is further provided,which comprises providing a first substrate, having a plurality ofparallel gate lines and a plurality of parallel signal lines formedthereon, wherein the gate lines and signal lines are perpendicular, apixel area is defined by two adjacent gate lines and two adjacent signallines, and a source electrode, electrically connected to one of the twoadjacent signal lines, and a drain electrode are formed on the pixelarea, forming a first pixel electrode, electrically connected to thedrain electrode, on the pixel area, providing a second substrate, havinga plurality of color-filtering areas and a second pixel electrode layerformed thereon, a predetermined distance above the first substrate,wherein a part of the second pixel electrode layer is relatively thin,aligning the first and second substrates such that each color-filteringarea on the second substrate corresponds to one pixel area located belowon the first substrate, and the part of the second pixel electrode layercorresponds to the signal lines located below on the first substrate,and finally combining the first and the second substrates.

According to the invention, the first and the second pixel electrode arenot limited to certain material, and are preferably made of indium tinoxide (ITO) or indium zinc oxide (IZO).

The relatively thin part of the second pixel electrode layer is formedby, for example, photolithography to thin or remove the correspondingpart of the pixel electrode layer, such that a thinned part, thinnerthan the pixel electrode layer, or a hollow part, is formed. Thethickness of the thinned part is not limited. As long as the part isthinned, i.e. thinner than the other part of the pixel electrode layer,the coupling capacitance between the pixel electrode layer and thesignal lines can be reduced, such that the object of the invention canbe fulfilled. Accordingly, thickness of the thinned part is preferablyzero, such that the pixel electrode in the area is preferably completelyremoved to be hollow.

According to the invention, the thinned or hollow part of the pixelelectrode layer is preferably segmented by the area, corresponding to apart of the signal lines, where the source electrode adjoins, into aplurality of striped areas.

According to the inventive liquid crystal display and fabricating methodthereof, capacitance loading of the signal lines is reduced by thinningof the corresponding pixel electrode, such that crosstalk resulting fromcoupling capacitance is reduced, and display quality is improved.

DESCRIPTION OF THE DRAWINGS

The present invention can be more fully understood by reading thesubsequent detailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1 is a top view showing a conventional TFT array substrate;

FIG. 2 is a cross-section taken at the line I—I in FIG. 1;

FIG. 3 is a cross-section taken at the line II—II in FIG. 1;

FIG. 4 illustrates the structure of the color filter substrate;

FIG. 5 is a cross-section of the TFT panel taken at the line II—II inFIG. 1;

FIGS. 6A–6D show the manufacturing process of TFT array substrate of theinvention; and

FIGS. 7A–7K show the manufacturing process of color filter substrate ofthe invention.

DETAILED DESCRIPTION OF THE INVENTION

Manufacture of TFT Array Substrate

FIGS. 6A–6D show the manufacturing process of TFT array substrate of theinvention. Bottom-gate type-TFT is used here to explain themanufacturing process, while top-gate type TFT is also applicable.

First, as in FIG. 6A, a substrate 0 of, for example, glass, is provided.A deposition step is performed thereon, followed by a firstphotolithography step, to form parallel gate lines 300, 301 in a rowdirection on the substrate 0, wherein the gate line 300 has a protrudingpart, which is the gate electrode 312. Next, a gate insulating layer 305(not shown) is formed on the gate lines 300, 301, gate electrode 312 andthe substrate 0. The gate lines 300, 301 and gate electrode 312 aremetal, formed by, for example, deposition. The gate insulating layer 305is, for example, SiO₂, SiN_(x), or silicon oxynitride, formed bydeposition.

In FIG. 6B, a deposition step is performed on the substrate, followed bya second photolithography step, to form a α-Si layer (below a n⁺ α-Silayer 313, not shown) and the n⁺ α-Si layer 313 on part of the gateinsulating layer 305, wherein the α-Si layer and n⁺ α-Si layer 313 forma α-Si semiconductor island on a TFT area 310.

In FIG. 6C, a conductive layer (not shown) is deposited on thesubstrate, and a third photolithography step is then performed thereonto remove part of the conductive layer, such that parallel signal lines400, 401 are formed in a columnar orientation on the gate insulatinglayer 305, and a source electrode 316 and a drain electrode 314 areformed on the n⁺ α-Si layer 313. Then, etching is performed, utilizingthe source electrode 316 and drain electrode 314 as a etching mask, toetch back part of the n⁺ α-Si layer 313 to reveal part of the surface ofthe α-Si layer, such that a thin film transistor structure in the TFTarea 310 is formed, wherein the source electrode 316 is electricallyconnected to the signal line 400.

FIG. 6D is a top view of the TFT array substrate of the invention. Afterthe thin film transistor in TFT area 310 is fabricated, a transparentphotoresist (not shown) is formed conformally on the substrate 0,followed by a photolithography step whereby a contact hole 307 above thedrain electrode 314 is formed to expose part of the surface of the drainelectrode 314.

Finally, a pixel electrode 801 of high-transparency and low-resistancematerial, e.g. ITO, is formed on a pixel area 306 to drive the molecularorientation of liquid crystals, wherein the pixel electrode 801 iselectrically connected to the drain electrode 304 via the contact hole307.

Manufacture of Color Filter Substrate

Currently, numerous methods have been developed to fabricate colorfilters, including pigment dispersion, dyeing, electrodeposition, andprinting. Of the invention, pigment dispersion is utilized to illustratethe manufacture of the color filter substrate.

FIGS. 7A–7K show the manufacturing process of color filter substrate ofthe invention.

In FIG. 7A, a glass substrate 0′ is provided with a light shieldinglayer 701 of, for example, Cr or black photo-sensitive resin formedthereon.

In FIG. 7B, the light shielding layer 701 is patterned byphotolithography to be matrix-shaped, as it is called black matrix (BM),to shield light and separate color-filtering resins of different colorto enhance color contrast.

Next, color-filtering units of red, green and blue are sequentiallyformed.

In FIG. 7C, a red resin is first spin-coated over the substrate 0′ toform a red color-filtering layer 702. Then, as in FIG. 7D,photolithography is performed to leave only the red resin in thepredetermined area.

In FIG. 7E, in the same manner, a blue and a green resin aresequentially spin-coated over the substrate 0′, and blue color-filteringunits 703 and green color-filtering units 704 are left in the respectivepredetermined pixel areas.

In FIG. 7F, a transparent planarization layer 705 is then formed on thesubstrate 0′. Then, as in FIG. 7G, a pixel electrode layer 706 of, forexample, transparent conductive material, e.g. ITO or IZO, is formed onthe planarization layer 705 to drive the molecular orientation of liquidcrystals. Then, as a critical step of the present invention, aphotoresist layer (not shown) is formed on the pixel electrode layer706, followed by a photolithography step to form a patterned area 707 onthe pixel electrode layer 706, as shown in FIG. 7H. FIG. 7I is a topview of the color filter substrate. The position of patterned area 707corresponds to that of the signal lines 400, 401 on the TFT arraysubstrate. The patterned area 707 is made up of a plurality of stripedareas, segmented by the area corresponding to a part of the signal lineswhere the TFT areas 310 adjoin. By controlling the etching rate or time,the patterned area 707 can be thinned, as shown in FIG. 7J, orcompletely removed to be hollow, as shown in FIG. 7H.

Cell Process

Next, as a normal fabricating process of LCD panel, the color filtersubstrate 0′ and TFT array substrate 0 are aligned and combined, suchthat each pixel area 306 corresponds to a color filtering unit 702, 703,or 704, the striped patterned area 707 is superimposed onto the signallines 400 and 401, and the part of pixel electrode layer 706, whichsegments the patterned area 707 into a plurality of striped areas,corresponding to the part of the signal lines where the TFT area 310adjoins. FIG. 7K shows a cross-section of the LCD panel.

Afterward, liquid crystal is filled into the LCD panel, following thesealing of the panel.

According to the manufacturing process described above, the LCD panelprovided includes, in the TFT array side, a substrate 0, parallel gatelines 300, 301 and parallel signal lines 400, 401, wherein the gatelines 300, 301 and signal lines 400, 401 are perpendicular, a pixel area306 is enclosed by the adjacent gate lines 300, 301 and adjacent signallines 400, 401, and a TFT area 310 is formed in the pixel area 306,having a source electrode 316 electrically connected to the signal line400. In addition, a pixel electrode 801 is formed on the pixel area 306.

Moreover, the LCD panel includes, in the color filter side, a substrate0′, provided with a black matrix 701, color-filtering units 702, 703,704, planarization layer 705, and a pixel electrode layer 706 with apatterned area 707. The patterned area 707 is made up of a plurality ofstriped areas, corresponding to the signal lines 400, 401 on the TFTarray substrate. In addition, the area segments the patterned area 707into striped areas corresponds to a part of the signal lines 400, 401where the TFT area 310 adjoins.

According to the LCD and fabricating method thereof, capacitance loadingof the signal lines is reduced by thinning the corresponding pixelelectrode, thereby crosstalk resulting from coupling capacitance isreduced, and display quality is improved.

The foregoing description has been presented for purposes ofillustration and description. Obvious modifications or variations arepossible in light of the above teaching. The embodiments were chosen anddescribed to provide the best illustration of the principles of thisinvention and its practical application to thereby enable those skilledin the art to utilize the invention in various embodiments and withvarious modifications as are suited to the particular use contemplated.All such modifications and variations are within the scope of thepresent invention as determined by the appended claims when interpretedin accordance with the breadth to which they are fairly, legally, andequitably entitled.

1. A liquid crystal display, comprising: a first substrate with aplurality of parallel gate lines and a plurality of parallel signallines formed thereon, wherein the gate lines and signal lines areperpendicular, and a pixel area is defined by two adjacent gate linesand two adjacent signal lines; a source electrode and a drain electrodeon the pixel area, wherein the source electrode is electricallyconnected to one of the two adjacent signal lines; a first pixelelectrode formed on the pixel area, electrically connected to the drainelectrode; a second substrate a predetermined distance above the firstsubstrate, having a plurality of color-filtering areas, each formeddirectly above the respective pixel area on the first substrate; and asecond pixel electrode layer on the second substrate, wherein the secondpixel electrode layer includes a patterned area directly above the,wherein the patterned area is thinned relative to an area of the secondpixel electrode layer that is not patterned signal lines.
 2. The liquidcrystal display as claimed in claim 1, wherein the second pixel layer isan indium tin oxide or indium zinc oxide layer.
 3. The liquid crystaldisplay as claimed in claim 1, wherein the first substrate or the secondsubstrate is glass.
 4. The liquid crystal display as claimed in claim 1,further comprising a liquid crystal layer filled between the first andsecond substrates.
 5. The liquid crystal display as claimed in claim 1,further comprising a gate electrode, electrically connected to one ofthe two adjacent gate lines, to link the source electrode and the drainelectrode.
 6. A liquid crystal display, comprising a first substratewith a plurality of parallel gate lines and a plurality of parallelsignal lines formed thereon, wherein the gate lines and signal lines areperpendicular, and a pixel area is defined by two adjacent gate linesand two adjacent signal lines; a source electrode and a drain electrodeon the pixel area, wherein the source electrode is electricallyconnected to one of the two adjacent signal lines; a first pixelelectrode formed on the pixel area, electrically connected to the drainelectrode; a second substrate a predetermined distance above the firstsubstrate, having a plurality of color-filtering areas, each formeddirectly above the respective pixel area on the first substrate; and asecond pixel electrode layer on the second substrate comprising aplurality of striped areas segmented by areas corresponding to parts ofthe signal lines where the source electrodes adjoin.
 7. The liquidcrystal display as claimed in claim 6, wherein the second pixel layer isan indium tin oxide or indium zinc oxide layer.
 8. The liquid crystaldisplay as claimed in claim 6, wherein the first substrate or the secondsubstrate is glass.
 9. The liquid crystal display as claimed in claim 6,further comprising a liquid crystal layer filled between the first andsecond substrates.
 10. The liquid crystal display as claimed in claim 6,further comprising a gate electrode, electrically connected to one ofthe two adjacent gate lines, to link the source electrode and the drainelectrode.
 11. A liquid crystal display, comprising a first substratewith a plurality of parallel gate lines and a plurality of parallelsignal lines formed thereon, wherein the gate lines and signal lines areperpendicular, and a pixel area is defined by two adjacent gate linesand two adjacent signal lines; a source electrode and a drain electrodeon the pixel area, wherein the source electrode is electricallyconnected to one of the two adjacent signal lines; a first pixelelectrode formed on the pixel area, electrically connected to the drainelectrode; a second substrate a predetermined distance above the firstsubstrate, having a plurality of color-filtering areas, each formeddirectly above the respective pixel area on the first substrate; and asecond pixel electrode layer above and substantially covering thecolor-filtering areas, wherein the portions of the second pixelelectrode layer directly above the signal lines are thinner than otherportions thereof.
 12. The liquid crystal display as claimed in claim 11,wherein the second pixel layer is an indium tin oxide or indium zincoxide layer.
 13. The liquid crystal display as claimed in claim 11,wherein the first substrate or the second substrate is glass.
 14. Theliquid crystal display as claimed in claim 11, further comprising aliquid crystal layer filled between the first and second substrates. 15.The liquid crystal display as claimed in claim 11, further comprising agate electrode, electrically connected to one of the two adjacent gatelines, to link the source electrode and the drain electrode.